This invention relates to detection apparatus, and more particularly, to a flammable gas detection system.
There are many gas detection systems and related equipment therefor such as found in U.S. Pat. Nos. 3,239,828; 3,522,010 and 3,665,240. Such prior art gas detection systems are useful in detecting the gas concentration level of a particular gas. In potentially hazardous areas, however, such as, for example, offshore platforms and chemical plants, it is highly desirable to have a detection system which not only indicates the concentration level of the gas, but also monitors the rate at which the gas concentration level is increasing in order to predict a hazardous condition before it occurs.
In some prior art gas detectors, it may take as much as 31/2 to 6 seconds or more to determine the existence of a hazardous concentration level in a high velocity air stream. It may take as much as 30 seconds to determine a hazardous concentration level in a static air stream. By the time such gas detectors determine that the level of gas concentration exceeds the LFL level or is dangerously high, the condition is already hazardous. It is therefore very desirable to have a rapid response detection system, which can be used in locations where rapid concentration build-ups can occur, such as an offshore platform or a chemical plant where a rupture could cause large volumes of flammable gases or vapors to reach the inlet of a pressurized heating and air conditioning system servicing a nonhazardous area, so that the condition can be remedied before it reaches a hazardous level.
As used in this application, the terms "hazardous rise rate", "hazardous rate of rise" and "hazardous rate of change" refer to a changing gas concentration level which would become hazardous if allowed to continue unchecked.
One object of this invention is to improve the safety of potentially hazardous areas.
Another object of this invention is to provide a detection system and method for predicting whether the gas concentration will approach a hazardous level.
A further object of this invention is to provide an alarm signal responsive to an increasing gas concentration level which would become hazardous if allowed to continue unchecked.
Another object of this invention is to provide improved circuitry for preventing false alarms, so as to avoid expensive and inconvenient shut downs.
It is still another object of this invention to provide an improved detection system of relatively simple design and construction, which is easy to use and install and results in considerable economic saving.
In accordance with the present invention, a detection apparatus is provided for use in monitoring a quantity whose rise rate or growth is an exponential, hyperbolic or linear function. The detection apparatus includes detection means for detecting the rate of the change of the quantity and comparator means for comparing that rate of change with a preselected reference rate of change. Control means operatively responsive to the comparing means are provided for effecting a signal indicating that the rate of change of the quantity has exceeded the preselected reference rise rate.
The detection apparatus may include sensing means for determining the absolute magnitude of the quantity, and second comparator means for comparing the absolute magnitude of the quantity with a preselected reference magnitude. The control means may further include limiting means operatively connected to the second comparator means for effecting generation of a signal only when the absolute magnitude of the quantity exceeds the preselected reference magnitude.
The detection apparatus can be constructed and arranged to include integrating means for effecting a signal dependent upon the period of time in which the rate of change of the quantity exceeds a preselected reference rate of change. Third comparative means are provided for determining whether the period of time is greater than the preselected period of time. The control means may further include second limiting means for effecting generation of the signal only when the period of time of rate of change of the quantity surpasses the predetermined period of time.
Furthermore, the detection apparatus may include selection means for determining the reference rate of change in response to preselected threshold and asymptotic values.
In the illustrated embodiment, a flammable gas detection system is provided with sensing means for determining the concentration level of a flammable gas. The sensing means includes a transducer for effecting an indicating signal proportional to the concentration of the gas. A differentiator is provided for generating a rate of change signal proportional to a preselected reference rate of change. Comparator means are provided for comparing the rate of change signal with the reference signal. Control means, operatively responsive to the comparing means, energizes an alarm signal, when the rate of change of the sensed gas concentration exceeds the reference rise rate.
In another embodiment, the flammable gas detection system includes means for effecting a reference signal porportional to a hazardous rate of change of the gas concentration level, including a threshold signal proportional to a preselected threshold value and an asymptotic signal proportional to a preselected asymptotic value. Comparator means are provided for comparing the gas concentration signal with the reference signal to determine if the rate of change of concentration of the sensed gas exceeds the hazardous rate of change.
The present invention also contemplates a method for monitoring a quantity, such as a flammable gas concentration, whose rise rate or growth is an exponential, hyperbolic or linear function. The method includes the steps of detecting the rise of the quantity, comparing the rate of change of the quantity with a reference rate of change effecting a signal when the rate of change of the quantity exceeds the reference rate of change.
A more detailed explanation of the invention is provided in the following description and claims and illustrated in the accompanying drawings.